Good luck. I got 'blessed' with short legs to I was able to build a box around my subs from my previous car. My seats are just not capable of moving very far back. I would say look into shallow mount subs and possibly building your own box. It is not that hard, I did it myself for mine. Is not the most professional looking, but it gets the job done and I'm pleased with it. And be prepared to sound deaden the back of the cab, you will need to.
Here are a few pics for good measure and because it's 3:15am here and I can't sleep.